Proxying slice access requests during a data evacuation

ABSTRACT

A method begins by a processing module receiving a checked write slice request from a requesting entity. The method continues by determining that locally stored encoded data slices do not include the requested encoded data slice. The method continues by identifying an alternate location for the requested encoded data slice. The method continues by determining whether the alternate location is associated with storage of the encoded data slice. The method continues when the alternate location is associated with the storage of the encoded data slice, by issuing a favorable checked write slice response to a requesting entity. The method can include facilitating transfer of the requested encoded data slice from the alternate location to the storage unit for storage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility Patent Application claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/199,816, entitled “STORING DATA AND ASSOCIATED METADATA IN A DISPERSED STORAGE NETWORK,” filed Jul. 31, 2015, which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

Technical Field of the Invention

This invention relates generally to computer networks and more particularly to dispersing error encoded data.

Description of Related Art

Computing devices are known to communicate data, process data, and/or store data. Such computing devices range from wireless smart phones, laptops, tablets, personal computers (PC), work stations, and video game devices, to data centers that support millions of web searches, stock trades, or on-line purchases every day. In general, a computing device includes a central processing unit (CPU), a memory system, user input/output interfaces, peripheral device interfaces, and an interconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using “cloud computing” to perform one or more computing functions (e.g., a service, an application, an algorithm, an arithmetic logic function, etc.) on behalf of the computer. Further, for large services, applications, and/or functions, cloud computing may be performed by multiple cloud computing resources in a distributed manner to improve the response time for completion of the service, application, and/or function. For example, Hadoop is an open source software framework that supports distributed applications enabling application execution by thousands of computers.

In addition to cloud computing, a computer may use “cloud storage” as part of its memory system. As is known, cloud storage enables a user, via its computer, to store files, applications, etc. on an Internet storage system. The Internet storage system may include a RAID (redundant array of independent disks) system and/or a dispersed storage system that uses an error correction scheme to encode data for storage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed or distributed storage network (DSN) in accordance with the present invention;

FIG. 2 is a schematic block diagram of an embodiment of a computing core in accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storage error encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an error encoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an error encoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of an encoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storage error decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an error decoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of an embodiment proxying slice access requests during a data evacuation in accordance with the present invention;

FIG. 9A is a schematic block diagram of another embodiment proxying slice access requests during a data evacuation in accordance with the present invention;

FIG. 9B is a schematic block diagram of another embodiment proxying slice access requests during a data evacuation in accordance with the present invention; and

FIG. 9C is a logic diagram of an example method proxying slice access requests during a data evacuation in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, or distributed, storage network (DSN) 10 that includes a plurality of computing devices 12-16, a managing unit 18, an integrity processing unit 20, and a DSN memory 22. The components of the DSN 10 are coupled to a network 24, which may include one or more wireless and/or wire lined communication systems; one or more non-public intranet systems and/or public interne systems; and/or one or more local area networks (LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may be located at geographically different sites (e.g., one in Chicago, one in Milwaukee, etc.), at a common site, or a combination thereof. For example, if the DSN memory 22 includes eight storage units 36, each storage unit is located at a different site. As another example, if the DSN memory 22 includes eight storage units 36, all eight storage units are located at the same site. As yet another example, if the DSN memory 22 includes eight storage units 36, a first pair of storage units are at a first common site, a second pair of storage units are at a second common site, a third pair of storage units are at a third common site, and a fourth pair of storage units are at a fourth common site. Note that a DSN memory 22 may include more or less than eight storage units 36. Further note that each storage unit 36 includes a computing core (as shown in FIG. 2, or components thereof) and a plurality of memory devices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and the integrity processing unit 20 include a computing core 26, which includes network interfaces 30-33. Computing devices 12-16 may each be a portable computing device and/or a fixed computing device. A portable computing device may be a social networking device, a gaming device, a cell phone, a smart phone, a digital assistant, a digital music player, a digital video player, a laptop computer, a handheld computer, a tablet, a video game controller, and/or any other portable device that includes a computing core. A fixed computing device may be a computer (PC), a computer server, a cable set-top box, a satellite receiver, a television set, a printer, a fax machine, home entertainment equipment, a video game console, and/or any type of home or office computing equipment. Note that each of the managing unit 18 and the integrity processing unit 20 may be separate computing devices, may be a common computing device, and/or may be integrated into one or more of the computing devices 12-16 and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to support one or more communication links via the network 24 indirectly and/or directly. For example, interface 30 supports a communication link (e.g., wired, wireless, direct, via a LAN, via the network 24, etc.) between computing devices 14 and 16. As another example, interface 32 supports communication links (e.g., a wired connection, a wireless connection, a LAN connection, and/or any other type of connection to/from the network 24) between computing devices 12 & 16 and the DSN memory 22. As yet another example, interface 33 supports a communication link for each of the managing unit 18 and the integrity processing unit 20 to the network 24.

Computing devices 12 and 16 include a dispersed storage (DS) client module 34, which enables the computing device to dispersed storage error encode and decode data as subsequently described with reference to one or more of FIGS. 3-8. In this example embodiment, computing device 16 functions as a dispersed storage processing agent for computing device 14. In this role, computing device 16 dispersed storage error encodes and decodes data on behalf of computing device 14. With the use of dispersed storage error encoding and decoding, the DSN 10 is tolerant of a significant number of storage unit failures (the number of failures is based on parameters of the dispersed storage error encoding function) without loss of data and without the need for a redundant or backup copies of the data. Further, the DSN 10 stores data for an indefinite period of time without data loss and in a secure manner (e.g., the system is very resistant to unauthorized attempts at accessing the data).

In operation, the managing unit 18 performs DS management services. For example, the managing unit 18 establishes distributed data storage parameters (e.g., vault creation, distributed storage parameters, security parameters, billing information, user profile information, etc.) for computing devices 12-14 individually or as part of a group of user devices. As a specific example, the managing unit 18 coordinates creation of a vault (e.g., a virtual memory block associated with a portion of an overall namespace of the DSN) within the DSTN memory 22 for a user device, a group of devices, or for public access and establishes per vault dispersed storage (DS) error encoding parameters for a vault. The managing unit 18 facilitates storage of DS error encoding parameters for each vault by updating registry information of the DSN 10, where the registry information may be stored in the DSN memory 22, a computing device 12-16, the managing unit 18, and/or the integrity processing unit 20.

The DSN managing unit 18 creates and stores user profile information (e.g., an access control list (ACL)) in local memory and/or within memory of the DSN memory 22. The user profile information includes authentication information, permissions, and/or the security parameters. The security parameters may include encryption/decryption scheme, one or more encryption keys, key generation scheme, and/or data encoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particular user, a user group, a vault access, public vault access, etc. For instance, the DSTN managing unit 18 tracks the number of times a user accesses a non-public vault and/or public vaults, which can be used to generate per-access billing information. In another instance, the DSTN managing unit 18 tracks the amount of data stored and/or retrieved by a user device and/or a user group, which can be used to generate per-data-amount billing information.

As another example, the managing unit 18 performs network operations, network administration, and/or network maintenance. Network operations includes authenticating user data allocation requests (e.g., read and/or write requests), managing creation of vaults, establishing authentication credentials for user devices, adding/deleting components (e.g., user devices, storage units, and/or computing devices with a DS client module 34) to/from the DSN 10, and/or establishing authentication credentials for the storage units 36. Network administration includes monitoring devices and/or units for failures, maintaining vault information, determining device and/or unit activation status, determining device and/or unit loading, and/or determining any other system level operation that affects the performance level of the DSN 10. Network maintenance includes facilitating replacing, upgrading, repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missing encoded data slices. At a high level, the integrity processing unit 20 performs rebuilding by periodically attempting to retrieve/list encoded data slices, and/or slice names of the encoded data slices, from the DSN memory 22. For retrieved encoded slices, they are checked for errors due to data corruption, outdated version, etc. If a slice includes an error, it is flagged as a ‘bad’ slice. For encoded data slices that were not received and/or not listed, they are flagged as missing slices. Bad and/or missing slices are subsequently rebuilt using other retrieved encoded data slices that are deemed to be good slices to produce rebuilt slices. The rebuilt slices are stored in the DSTN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core 26 that includes a processing module 50, a memory controller 52, main memory 54, a video graphics processing unit 55, an input/output (IO) controller 56, a peripheral component interconnect (PCI) interface 58, an IO interface module 60, at least one IO device interface module 62, a read only memory (ROM) basic input output system (BIOS) 64, and one or more memory interface modules. The one or more memory interface module(s) includes one or more of a universal serial bus (USB) interface module 66, a host bus adapter (HBA) interface module 68, a network interface module 70, a flash interface module 72, a hard drive interface module 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operating system (OS) file system interface (e.g., network file system (NFS), flash file system (FFS), disk file system (DFS), file transfer protocol (FTP), web-based distributed authoring and versioning (WebDAV), etc.) and/or a block memory interface (e.g., small computer system interface (SCSI), internet small computer system interface (i SCSI), etc.). The DSN interface module 76 and/or the network interface module 70 may function as one or more of the interface 30-33 of FIG. 1. Note that the IO device interface module 62 and/or the memory interface modules 66-76 may be collectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storage error encoding of data. When a computing device 12 or 16 has data to store it disperse storage error encodes the data in accordance with a dispersed storage error encoding process based on dispersed storage error encoding parameters. The dispersed storage error encoding parameters include an encoding function (e.g., information dispersal algorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding, non-systematic encoding, on-line codes, etc.), a data segmenting protocol (e.g., data segment size, fixed, variable, etc.), and per data segment encoding values. The per data segment encoding values include a total, or pillar width, number (T) of encoded data slices per encoding of a data segment i.e., in a set of encoded data slices); a decode threshold number (D) of encoded data slices of a set of encoded data slices that are needed to recover the data segment; a read threshold number (R) of encoded data slices to indicate a number of encoded data slices per set to be read from storage for decoding of the data segment; and/or a write threshold number (W) to indicate a number of encoded data slices per set that must be accurately stored before the encoded data segment is deemed to have been properly stored. The dispersed storage error encoding parameters may further include slicing information (e.g., the number of encoded data slices that will be created for each data segment) and/or slice security information (e.g., per encoded data slice encryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as the encoding function (a generic example is shown in FIG. 4 and a specific example is shown in FIG. 5); the data segmenting protocol is to divide the data object into fixed sized data segments; and the per data segment encoding values include: a pillar width of 5, a decode threshold of 3, a read threshold of 4, and a write threshold of 4. In accordance with the data segmenting protocol, the computing device 12 or 16 divides the data (e.g., a file (e.g., text, video, audio, etc.), a data object, or other data arrangement) into a plurality of fixed sized data segments (e.g., 1 through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more). The number of data segments created is dependent of the size of the data and the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a data segment using the selected encoding function (e.g., Cauchy Reed-Solomon) to produce a set of encoded data slices. FIG. 4 illustrates a generic Cauchy Reed-Solomon encoding function, which includes an encoding matrix (EM), a data matrix (DM), and a coded matrix (CM). The size of the encoding matrix (EM) is dependent on the pillar width number (T) and the decode threshold number (D) of selected per data segment encoding values. To produce the data matrix (DM), the data segment is divided into a plurality of data blocks and the data blocks are arranged into D number of rows with Z data blocks per row. Note that Z is a function of the number of data blocks created from the data segment and the decode threshold number (D). The coded matrix is produced by matrix multiplying the data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encoding with a pillar number (T) of five and decode threshold number of three. In this example, a first data segment is divided into twelve data blocks (D1-D12). The coded matrix includes five rows of coded data blocks, where the first row of X11-X14 corresponds to a first encoded data slice (EDS 1_1), the second row of X21-24 corresponds to a second encoded data slice (EDS 2_1), the third row of X31-X34 corresponds to a third encoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to a fourth encoded data slice (EDS 4_1), and the fifth row of X51-X54 corresponds to a fifth encoded data slice (EDS 5_1). Note that the second number of the EDS designation corresponds to the data segment number.

Returning to the discussion of FIG. 3, the computing device also creates a slice name (SN) for each encoded data slice (EDS) in the set of encoded data slices. A typical format for a slice name 60 is shown in FIG. 6. As shown, the slice name (SN) 60 includes a pillar number of the encoded data slice (e.g., one of 1-T), a data segment number (e.g., one of 1-Y), a vault identifier (ID), a data object identifier (ID), and may further include revision level information of the encoded data slices. The slice name functions as, at least part of, a DSN address for the encoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces a plurality of sets of encoded data slices, which are provided with their respective slice names to the storage units for storage. As shown, the first set of encoded data slices includes EDS 1_1 through EDS 5_1 and the first set of slice names includes SN 1_1 through SN 5_1 and the last set of encoded data slices includes EDS 1_Y through EDS 5Y and the last set of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storage error decoding of a data object that was dispersed storage error encoded and stored in the example of FIG. 4. In this example, the computing device 12 or 16 retrieves from the storage units at least the decode threshold number of encoded data slices per data segment. As a specific example, the computing device retrieves a read threshold number of encoded data slices.

To recover a data segment from a decode threshold number of encoded data slices, the computing device uses a decoding function as shown in FIG. 8. As shown, the decoding function is essentially an inverse of the encoding function of FIG. 4. The coded matrix includes a decode threshold number of rows (e.g., three in this example) and the decoding matrix in an inversion of the encoding matrix that includes the corresponding rows of the coded matrix. For example, if the coded matrix includes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2, and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a schematic block diagram of proxying slice access requests during a data evacuation. Data evacuation is a process by which a first ds unit is removed from the system, a second ds unit is added to the system to replace the first ds unit, and the first ds unit proceeds to write all of its slices as quickly as possible to the second ds unit. This enables replacement of a faulty or otherwise inadequate ds unit with a new one while minimizing rebuilding, which is considerably more expensive in terms of network and processing resources. However, it suffers from several issues: slices that are deleted are still transferred over the network wasting time and resources, slices that are not yet transferred over cannot be read, reducing availability and reliability, checked write operations will not check against the correct version if it has not yet been transferred and listing requests return empty results, causing unnecessary rebuilding to occur. These issues may be prevented or eliminated by introducing proxying of requests from the second ds unit to the first ds unit, during the period the evacuation takes place.

When the second ds unit receives a read request for a slice it does not have, and if the evacuation is ongoing, it may transmit an identical read request to the first ds unit, and use the returned result to formulate a read response to return to the original requester. If the second ds unit receives a write request for a slice it does not have, and the request is a checked write the second ds unit may send a CheckRequest to the first ds unit, and use the response to apply the check condition for the slice it received. If the check succeeds, then it processes the write successfully, otherwise the second ds unit fails the write request with a check condition error. If the second ds unit receives a finalize/undo request for a slice it has, it may proxy these for the first ds unit which will delete the slice, and prevent it from having to be transferred over the network. If the second ds unit receives a list request, it may proxy the list request to the first ds unit and combines its listing results with the results obtained from running that same list locally.

By proxying the above requests in the following ways, evacuation is sped up, unnecessary rebuilding is prevented, and read and checked write requests will operate as expected. Once the evacuation is completed, normal behavior resumes and the second ds unit stops proxying requests.

FIG. 9 shows a dispersed storage network (DSN) 10 that includes the distributed storage and task (DST) processing unit 16 of FIG. 1, the network 24 of FIG. 1, and at least two storage units (DS unit 1 and DS unit 2). The DST processing unit 16 includes the DST client module 34 of FIG. 1. As shown, slices are to be transferred between DS unit 1 (evacuation storage unit) to DS unit 2 (replacement/target storage unit). Each storage unit includes at least DS client module 34 of FIG. 1, and a memory 88. The memory 88 may be implemented utilizing one or more of solid-state memory, magnetic disk drive memory, optical disk drive memory, etc. Each DS unit may be implemented utilizing the DST execution unit 36 of FIG. 1. Hereafter, each DST execution unit may be interchangeably referred to as a storage unit or DS unit and a storage set may be interchangeably referred to as a set of storage units or as a set of DS units. The DSN functions to store data.

In an example of operation of evacuation and replacement, a storage unit, for example, DS unit 2 receives a checked write request from the DST processing unit 16. For example, the DST client module 34 of DST processing unit 16 selects DS unit 2 to access to an encoded data slice (during evacuation of DS unit 1), generates a checked write slice request 1 that includes one or more of the encoded data slice and a slice name associated with the encoded data slice, and sends, via the network 24, the checked write slice request 1 to the DS unit 2.

FIG. 9A is a schematic block diagram of another embodiment proxying slice access requests during a data evacuation in accordance with the present invention. As shown, having received the checked write request 1, DS unit 2 determines that locally stored encoded data slices 422 do not include the requested encoded data slice. For instance, the DST client module 34 of the DS unit 2 determines that the encoded data slices stored in the memory 88 of the DS unit 2 do not include the requested encoded data slices as DS unit 1 has not completed moving slices from the memory 88 of the DS unit 1 to the memory 88 of DS unit 2, in accordance with an initiated evacuation.

Having determined that the locally stored encoded data slices to not include the requested encoded data slice, DS unit 2 determines at least one alternate location for the requested encoded data slice (i.e., DS unit 1). For example, the DST client module 34 of DS unit 2 sends, via the network 24, a checked request 1 to DS unit 1 and receives, via the network 24, a checked response 1 from the DS unit 1, and interprets the checked response 1 to indicate whether the at least one alternate location is associated with the requested encoded data slice.

When the at least one alternate location is associated with the storage of the encoded data slice, DS unit 2 issues a checked response 1 to DS processing unit 16, where the checked response 1 indicates successful access to the requested encoded data slice. For example, the DST client module 34 generates the checked response 1 to include one or more of a code associated with the checked write slice request (e.g., a unique serial identifier) the slice name, and revision level, and sends, via the network 24, the checked response 1 to the DST processing unit 16.

FIG. 9B is a schematic block diagram of another embodiment proxying slice access requests during a data evacuation in accordance with the present invention. As shown, alternatively, or in addition to, DST processing unit 16 facilitates transfer of requested encoded data slices from the alternate location (DS unit 1) to DS unit 2 for storage. For the example, the DST client module 34 of DS unit 2 sends a read slice request to the DST client module 34 of DS unit 1 for the encoded data slice, receives a transfer slice 1 as the encoded data slice, and stores the encoded data slice in the memory 88 of the DS unit 2.

FIG. 9C is a flowchart illustrating an example of proxying slice access requests during a data evacuation. In particular, a method is presented for use in conjunction with one or more functions and features described in conjunction with FIGS. 1-9B, and also FIG. 9C. The method begins at step 900 where a processing module (DST processing unit 16) of a computing device of one or more computing devices of a dispersed storage network initiates an evacuation of encoded storage slices from a first storage unit to a second storage unit.

Selecting a replacement storage unit candidate to receive evacuated encoded data slices from a first storage unit can be based on any of: newly commissioned storage units, specific hardware requirements, IO requirements, speed requirements, storage capacity, historical reliability, traffic levels, geographic location, or decided by a decentralized agreement module.

A decentralized agreement module receives a ranked scoring information request from a requesting entity with regards to a set of candidate resources. For each candidate resource, the decentralized agreement module performs a deterministic function on a location identifier (ID) of the candidate resource and an asset ID of a ranked scoring information request to produce an interim result. As a specific example, the decentralized agreement module combines the asset ID and the location ID of the candidate resource to produce a combined value and performs a hashing function on the combined value to produce the interim result.

For each interim result, the decentralized agreement module performs a normalizing function on the interim result to produce a normalized interim result. As a specific example, the decentralized agreement module obtains a permutation value associated with the deterministic function (e.g., maximum number of permutations of output of the deterministic function) and divides the interim result by the permutation value to produce the normalized interim result (e.g., with a value between 0 and 1).

For each normalized interim result, the decentralized agreement module performs a scoring function on the normalized interim result utilizing a location weight associated with the candidate resource associated with the interim result to produce a score of a set of scores. As a specific example, the decentralized agreement module divides the location weight by a negative log of the normalized interim result to produce the score.

The decentralized agreement module rank orders the set of scores to produce ranked scoring information (e.g., ranking a highest value first). The decentralized agreement module outputs the ranked scoring information to the requesting entity. The requesting entity may utilize the ranked scoring information to select one storage unit from a plurality of storage units.

The method continues at step 902 where a processing module (DST client module 34) of a computing device of one or more computing devices of a dispersed storage network receives a checked write slice request from a requesting entity (e.g., DS unit 2). The method continues at step 904 where the processing module determines that locally stored encoded data slices do not include the requested encoded data slice. For example, the processing module performs a lookup or interprets a query response.

The method continues at step 906 where the processing module identifies an alternate location for the requested encoded data slice (e.g., DS unit 1).

The method continues at step 908 where the processing module determines whether the alternate location is associated with storage of the encoded data slice. For example, the processing module issues a checked request to the alternate location, interprets a checked response, and indicates that the requested encoded data slice is located at the alternate storage location when the checked response indicates storage of the encoded data slice.

When the alternate location is associated with the storage of the requested encoded data slice, the method continues at step 910 where the processing module issues a favorable checked write slice response to a requesting entity. For example, the processing module generates the response to include one or more of a code associated with the checked write slice request, a slice name and revision level.

Alternatively, or in addition to, the processing module facilitates, in step 912, transfer of the requested encoded data slice from the alternate location for local storage.

The method described above in conjunction with the computing device and the storage units can alternatively be performed by other modules of the dispersed storage network or by other devices. For example, any combination of a first module, a second module, a third module, a fourth module, etc. of the computing device and the storage units may perform the method described above. In addition, at least one memory section (e.g., a first memory section, a second memory section, a third memory section, a fourth memory section, a fifth memory section, a sixth memory section, etc. of a non-transitory computer readable storage medium) that stores operational instructions can, when executed by one or more processing modules of one or more computing devices and/or by the storage units of the dispersed storage network (DSN), cause the one or more computing devices and/or the storage units to perform any or all of the method steps described above.

It is noted that terminologies as may be used herein such as bit stream, stream, signal sequence, etc. (or their equivalents) have been used interchangeably to describe digital information whose content corresponds to any of a number of desired types (e.g., data, video, speech, audio, etc. any of which may generally be referred to as ‘data’).

As may be used herein, the terms “substantially” and “approximately” provides an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to fifty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As may also be used herein, the term(s) “configured to”, “operably coupled to”, “coupled to”, and/or “coupling” includes direct coupling between items and/or indirect coupling between items via an intervening item (e.g., an item includes, but is not limited to, a component, an element, a circuit, and/or a module) where, for an example of indirect coupling, the intervening item does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As may further be used herein, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two items in the same manner as “coupled to”. As may even further be used herein, the term “configured to”, “operable to”, “coupled to”, or “operably coupled to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform, when activated, one or more its corresponding functions and may further include inferred coupling to one or more other items. As may still further be used herein, the term “associated with”, includes direct and/or indirect coupling of separate items and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that a comparison between two or more items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1. As may be used herein, the term “compares unfavorably”, indicates that a comparison between two or more items, signals, etc., fails to provide the desired relationship.

As may also be used herein, the terms “processing module”, “processing circuit”, “processor”, and/or “processing unit” may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The processing module, module, processing circuit, and/or processing unit may be, or further include, memory and/or an integrated memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of another processing module, module, processing circuit, and/or processing unit. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that if the processing module, module, processing circuit, and/or processing unit includes more than one processing device, the processing devices may be centrally located (e.g., directly coupled together via a wired and/or wireless bus structure) or may be distributedly located (e.g., cloud computing via indirect coupling via a local area network and/or a wide area network). Further note that if the processing module, module, processing circuit, and/or processing unit implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory and/or memory element storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Still further note that, the memory element may store, and the processing module, module, processing circuit, and/or processing unit executes, hard coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in one or more of the Figures. Such a memory device or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of method steps illustrating the performance of specified functions and relationships thereof. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for convenience of description. Alternate boundaries and sequences can be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are thus within the scope and spirit of the claims. Further, the boundaries of these functional building blocks have been arbitrarily defined for convenience of description. Alternate boundaries could be defined as long as the certain significant functions are appropriately performed. Similarly, flow diagram blocks may also have been arbitrarily defined herein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence could have been defined otherwise and still perform the certain significant functionality. Such alternate definitions of both functional building blocks and flow diagram blocks and sequences are thus within the scope and spirit of the claims. One of average skill in the art will also recognize that the functional building blocks, and other illustrative blocks, modules and components herein, can be implemented as illustrated or by discrete components, application specific integrated circuits, processors executing appropriate software and the like or any combination thereof

In addition, a flow diagram may include a “start” and/or “continue” indication. The “start” and “continue” indications reflect that the steps presented can optionally be incorporated in or otherwise used in conjunction with other routines. In this context, “start” indicates the beginning of the first step presented and may be preceded by other activities not specifically shown. Further, the “continue” indication reflects that the steps presented may be performed multiple times and/or may be succeeded by other activities not specifically shown. Further, while a flow diagram indicates a particular ordering of steps, other orderings are likewise possible provided that the principles of causality are maintained.

The one or more embodiments are used herein to illustrate one or more aspects, one or more features, one or more concepts, and/or one or more examples. A physical embodiment of an apparatus, an article of manufacture, a machine, and/or of a process may include one or more of the aspects, features, concepts, examples, etc. described with reference to one or more of the embodiments discussed herein. Further, from figure to figure, the embodiments may incorporate the same or similarly named functions, steps, modules, etc. that may use the same or different reference numbers and, as such, the functions, steps, modules, etc. may be the same or similar functions, steps, modules, etc. or different ones.

Unless specifically stated to the contra, signals to, from, and/or between elements in a figure of any of the figures presented herein may be analog or digital, continuous time or discrete time, and single-ended or differential. For instance, if a signal path is shown as a single-ended path, it also represents a differential signal path. Similarly, if a signal path is shown as a differential path, it also represents a single-ended signal path. While one or more particular architectures are described herein, other architectures can likewise be implemented that use one or more data buses not expressly shown, direct connectivity between elements, and/or indirect coupling between other elements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of the embodiments. A module implements one or more functions via a device such as a processor or other processing device or other hardware that may include or operate in association with a memory that stores operational instructions. A module may operate independently and/or in conjunction with software and/or firmware. As also used herein, a module may contain one or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes one or more memory elements. A memory element may be a separate memory device, multiple memory devices, or a set of memory locations within a memory device. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. The memory device may be in a form a solid state memory, a hard drive memory, cloud memory, thumb drive, server memory, computing device memory, and/or other physical medium for storing digital information.

While particular combinations of various functions and features of the one or more embodiments have been expressly described herein, other combinations of these features and functions are likewise possible. The present disclosure is not limited by the particular examples disclosed herein and expressly incorporates these other combinations. 

What is claimed is:
 1. A method for execution by one or more processing modules of one or more computing devices of a dispersed storage network (DSN), the method comprises: initiating an evacuation of encoded data slices from a first storage unit to a second storage unit; receiving, at the second storage unit, a checked write slice request from a requesting entity, the checked write slice request including a requested encoded data slice; determining that locally stored encoded data slices do not include the requested encoded data slice; identifying an alternate location for the requested encoded data slice; determining whether the alternate location is associated with storage of the requested encoded data slice; and when the alternate location is associated with storage of the requested encoded data slice, issuing a favorable checked write slice response to the requesting entity.
 2. The method of claim 1, wherein the checked write slice request further includes one or more of: slice name, encoded data slice for storage, or a revision level.
 3. The method of claim 2 further comprising generating a response to include one or more of: a code associated with the checked write slice request, a name of the encoded data slice, or a revision level.
 4. The method of claim 1, wherein the determining that locally stored encoded data slices do not include the requested encoded data slice includes one or more of: performing a lookup or interpreting a query response.
 5. The method of claim 1, wherein the determining whether the alternate location is associated with the requested encoded data slice includes one or more of: issuing a checked request to the alternate location or interpreting a checked response.
 6. The method of claim 1 further comprising facilitating transfer of the requested encoded data slice from the alternate location to a location of the locally stored encoded data slices for storage.
 7. The method of claim 1 further comprising selecting the second storage unit based on any of: newly commissioned storage units, specific hardware requirements, IO requirements, speed requirements, storage capacity, historical reliability, traffic levels, geographic location, or a decentralized agreement module decision.
 8. The method of claim 7, wherein the decentralized agreement module receives a ranked scoring information request from a requestor with regards to a set of candidate storage unit resources and, for each of the candidate storage unit resources, the decentralized agreement module performs a deterministic function on a location identifier (ID) of the candidate storage unit resource and an asset ID of the ranked scoring information request.
 9. A computing device of a group of computing devices of a dispersed storage network (DSN), the computing device comprises: an interface; a local memory; and a processing module operably coupled to the interface and the local memory, wherein the processing module functions to: initiate an evacuation of encoded data slices from a first storage unit to a second storage unit; receive, at the second storage unit, a checked write slice request from a requesting entity, the checked write slice request including a requested encoded data slice; determine that locally stored encoded data slices do not include the requested encoded data slice; identify an alternate location for the requested encoded data slice; determine whether the alternate location is associated with storage of the requested encoded data slice; and when the alternate location is associated with storage of the requested encoded data slice, issue a favorable checked write slice response to the requesting entity.
 10. The computing device of claim 9, wherein the checked write slice request further includes one or more of: slice name, encoded data slice for storage, or a revision level.
 11. The computing device of claim 9 further comprising generating a response to include one or more of: a code associated with the checked write slice request, a name of the encoded data slice, or a revision level.
 12. The computing device of claim 9, wherein the determining that locally stored encoded data slices do not include the requested encoded data slice includes one or more of: performing a lookup or interpreting a query response.
 13. The computing device of claim 9, wherein the determining whether the alternate location is associated with the requested encoded data slice includes one or more of: issuing a checked request to the alternate location or interpreting a checked response.
 14. The computing device of claim 9 further comprising facilitating transfer of the requested encoded data slice from the alternate location to a location of the locally stored encoded data slices for storage.
 15. A method for execution by one or more processing modules of one or more computing devices of a dispersed storage network (DSN), the method comprises: receiving, during an evacuation of encoded data slices from a first storage unit to a second storage unit, a checked write slice request at the second storage unit from a requesting entity, the checked write slice request including a requested encoded data slice; determining that locally stored encoded data slices do not include the requested encoded data slice; identifying an alternate location for the requested encoded data slice; determining whether the alternate location is associated with storage of the requested encoded data slice; and when the alternate location is associated with storage of the requested encoded data slice, issuing a favorable checked write slice response to the requesting entity.
 16. The method of claim 15, wherein the checked write slice request further includes one or more of: slice name, encoded data slice for storage, or a revision level.
 17. The method of claim 15 further comprising generating a response to include one or more of: a code associated with the checked write slice request, a name of the encoded data slice, or a revision level.
 18. The method of claim 15, wherein the determining that locally stored encoded data slices do not include the requested encoded data slice includes one or more of: performing a lookup or interpreting a query response.
 19. The method of claim 15, wherein the determining whether the alternate location is associated with the requested encoded data slice includes one or more of: issuing a checked request to the alternate location or interpreting a checked response.
 20. The method of claim 15 further comprising facilitating transfer of the requested encoded data slice from the alternate location to a location of the locally stored encoded data slices for storage. 